All law is complicated, unfortunately.
Complicated in its wording and, more so, especially with the "laws of war" extremely complicated in practice.
Easy to understand that you do not torture or kill prisoners and the like but other laws are not so clear cut.
A lot of them assume two armies facing each other over empty ground. A lot of fighting now takes place in built up areas with long-range artillery, missiles, and strikes from the air.
Under the laws of war, combatants are required to be members of a proper military organisation and wear recognisable uniforms. When they are not and do not and your enemy are just armed civilians (for example, may be a thirteen-year-old with a rocket launcher) it gets murky. Even murkier when they are deliberately using hospitals and other civilian infrastructure as cover.
There seems to be a perception that you cannot wage war if it may involve civilian casualties. That is a noble idea (more noble of course, would be to sort out our differences without violence). However, the requirement is that you do not deliberately directly target non-combatants and take all precautions to safe guard them. In practice, non-combatants and their property become "collateral damage" and this is usually justified by claiming that the target was a combatant and any other "collateral damage" was incidental.